Tappet thickness - previous posts

[lyons]

On searching previous posts about reducing the thickness below the smallest available 0.085 tappet shim, but there is no reply.

Inlet side is all shimmed up but on the exhaust side although 1-3 valves are now correctly gapped, but 4-6 are way below showing 0.020 instead of the recommended 0.06.

I know that tappet shims are hardened all the way through and there must be sufficient thickness left to stop the carriers impacting the spring retaining collars.

So - can I reduce pad thickness from 0.085 to 0.080 or less, even 0.077.

Alternative listed is to skim inside of pad carriers, has anyone done this ?

Head has been skimmed flat and new valves fitted.

[MarekH]

I don't think anyone is going to "take the drop" and advise you that it is safe to do so. I think what you have to consider is that you don't want the shims to rock about, float or to break.

Three things can be considered:-

1/ Use lash caps;
2/ Grind some material of the top off of the cam buckets;
3/ Usually people end up grinding the ends off of the valve stems.

The cam buckets in the 6l v12 and in the AJ16 engines after that are significantly lighter than the usual ones you see. This is by virtue of having less thickness on top and the contact spot inside is smaller, despite being the same overall thickness at this point as the earlier tappets.

kind regards
Marek

[mgcjag]

Are you measureing the gaps correctly....you mention 0.06.......should be 0.004in and .006in depending on what model your car is

[abowie]

Your options are to get some shims made to the correct thickness, get the top of the valve stem skimmed to shorten it or to get the valve seats replaced and recut to the correct height which is what I'd do if the head is currently off the car.

[christopher storey]

Am I going crackers ? If you have excessive tappet clearance of 20 thou instead of 6 thou, what you need are shims 14 thou thicker than the existing ones don't you ? You only need undersize shims where there has been valve seat recession and you cannot get sufficient clearance

[paulsco]

Hi Christopher,

I think Lyons means two thou.

Paul

[mgcjag]

You never know...he might even be useing metric... Steve

[Geoff Green]

Be careful grinding the top of the valve stem because you cannot lower it below the spring retainer. The shim must rest on the top of the valve stem and not bottom of the recess in the spring retainer.

If the shim pushes on the retainer rather than the valve stem it will loosen and wear the keepers and spring retainer. I have seen the stem an pieces pull through the spring retainer and drop into the piston.

The spring retainer catches the edge of the shim and keeps it centered over the top of the valve stem.